On Tue, 17 Jan 2012 20:51:13 +0200 (EET)
Pekka Enberg <penberg@xxxxxxxxxx> wrote:
> Ok, so here's a proof of concept patch that implements sample-base
> per-process free threshold VM event watching using perf-like syscall ABI.
> I'd really like to see something like this that's much more extensible and
> clean than the /dev based ABIs that people have proposed so far.
OK, so I'm slow, but better late than never. I plead travel.
I guess the thing that surprises me is that nobody has said this yet: this
looks a lot like an event-reporting mechanism like perf. Is there a reason
these can't be perf-style events integrated with all the rest?
> +struct vmnotify_config {
> + /*
> + * Size of the struct for ABI extensibility.
> + */
> + __u32 size;
> +
> + /*
> + * Notification type bitmask
> + */
> + __u64 type;
> +
> + /*
> + * Free memory threshold in percentages [1..99]
> + */
> + __u32 free_threshold;
Is this an upper-bound threshold or a lower-bound threshold? From your
example, it looks like "free_threshold" is "the amount of memory that is
not free", which seems confusing.
[...]
> new file mode 100644
> index 0000000..6800450
> --- /dev/null
> +++ b/mm/vmnotify.c
> @@ -0,0 +1,235 @@
> +#include <linux/anon_inodes.h>
> +#include <linux/vmnotify.h>
> +#include <linux/syscalls.h>
> +#include <linux/file.h>
> +#include <linux/list.h>
> +#include <linux/poll.h>
> +#include <linux/slab.h>
> +#include <linux/swap.h>
> +
> +#define VMNOTIFY_MAX_FREE_THRESHOD 100
Did we run out of L's here? :)
> +static ssize_t vmnotify_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
> +{
> + struct vmnotify_watch *watch = file->private_data;
> + int ret = 0;
> +
> + mutex_lock(&watch->mutex);
> +
> + if (!watch->pending)
> + goto out_unlock;
> +
> + if (copy_to_user(buf, &watch->event, sizeof(struct vmnotify_event))) {
> + ret = -EFAULT;
> + goto out_unlock;
> + }
> +
> + ret = watch->event.size;
> +
> + watch->pending = false;
> +
> +out_unlock:
> + mutex_unlock(&watch->mutex);
> +
> + return ret;
> +}
So this is a nonblocking-only interface? That may surprise some
developers. You already have a wait queue, why not wait on it if need be?
> +static int vmnotify_copy_config(struct vmnotify_config __user *uconfig,
> + struct vmnotify_config *config)
> +{
> + int ret;
> +
> + ret = copy_from_user(config, uconfig, sizeof(struct vmnotify_config));
> + if (ret)
> + return -EFAULT;
> +
> + if (!config->type)
> + return -EINVAL;
> +
> + if (config->type & VMNOTIFY_TYPE_SAMPLE) {
> + if (config->sample_period_ns < NSEC_PER_MSEC)
> + return -EINVAL;
> + }
What happens if the sample period is zero?
jon
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